Butterfly wing patterns create powerful illusory motion cues

The dazzling stripes found on zebras and snakes have long been thought to interfere with predator motion perception, but this hypothesis has received little empirical support to date. Butterflies demonstrate enormously diverse and high-contrast wing patterns, the function of which has inspired intense theoretical debate and research. Here we suggest that butterfly wing patterns work in tandem with flight dynamics to create visual illusions that confuse predators. We use multiple independent lines of enquiry with biologically inspired modelling to support this hypothesis: free-flight butterfly take-offs filmed at high speed demonstrate the creation of misleading motion cues; phylogenetically controlled analyses demonstrate that this is an evolutionarily widespread strategy; and in silico evolution experiments independently converge on butterfly-like wing patterns. Our results show that butterfly wing patterns and flight dynamics create powerful illusory motion effects, potentially representing one of the most successful and hitherto unknown visual defence strategies in moving animals.